Martin Joseph Wayne
Engineering at Williston Rd, Gainesville, FL

4771233, Sep 13, 1988

Jan 29, 1987

7/007979

Martin J. Wayne - Gainesville FL

G01R 1900, G01R 1073

324 99R

An ammeter is used for measuring the current flowing through a lead on a printed circuit board having a four point probe contacting the printed wire under test. Each probe points is spring loaded and approximately one millimeter separates adjacent probe points. The center two probe points are coupled to the inputs of a high gain chopper stabilized operational amplifier which provides a signal related to the voltage between the center two probe points as a result of the line resistance. The operational amplifier must have a very low and stable input offset voltage. The amplifier signal is applied to the base electrodes of a bipolar current driver circuit, such as two opposite polarity Darlington circuits, which respectively have a source of positive and negative voltage coupled to flow through the collector emitter electrodes when the signal applied to the base renders the collector emitter conductive. The two sources of opposite polarity voltage are each coupled to a common point on the side thereof remote from the Darlington transistors. The emitters of the Darlington circuits are coupled together and to one of the outer probe points.